This disclosure relates to an electrophoretic display device.
Reflective displays can realize flexible displays with low costs, and show low power consumption. Therefore, reflective displays are often used as display devices in low power mobile displays. The reflective displays can be electrophoretic displays (EPDs), liquid crystal displays (LCDs), electrowetting displays (EWD), and electrochromic displays (ECD). Among the above, the most advanced reflective display is the EPD that uses movements of particles to effect a reflective display.
Since the reflective display displays images by reflecting external lights, the reflective display can be used only when the external lights exist, and cannot be used in a dark space without external light. It is therefore difficult to use such displays at night. Therefore, a display device that operates as a light emission display where there is no external light is desired.
U.S. Pat. No. 6,727,881 discloses an electrophoretic display, in which a capsule includes electroluminescence (EL) particles and particles blocking the light emitted from the EL particles. In this display, light of desired color can be emitted or blocked in the light emission mode. However, light of a desired color cannot be reflected or blocked in the reflection mode.
U.S. Patent Application Publication No. 20040150613 discloses an electrophoretic display that includes reflective particles and photoluminescence (PL) particles having same charges that are disposed in a cell. In this display, when a voltage is applied to an electrode, the reflective particles and the PL particles move simultaneously. In the light emission mode, the two types of particles are located on an upper portion of a pixel by the applied voltage, and ultraviolet (UV) rays are irradiated from a backlight unit (BLU) to emit the light of desired color. In addition, if the color representation is not desired, the BLU is turned off. However, in the reflection mode, when the voltage is applied so that the two types of particles can locate on the upper portion of the pixel, the reflective particles interact with external light and produce a color that is a composite of the external light and that produced by the particles. In this display device, among the particles located on the upper portion of the pixel, the PL particles contribute to the display of images only in the light emission mode and the reflective particles contribute to the display of images in the reflection mode only. This operational property causes a degradation of color emission due to the PL particles or the reflective particles that do not participate in the color emission, when the color is emitted in the light emission mode or in the reflection mode.